This invention relates to batteries for portable radios and other electronic devices. More particularly, the invention relates to batteries which include apparatus for enabling current sensing by a portable radio device or other energy consuming device which is attachable thereto.
To provide electrical energy to portable radio devices, an electrical battery is coupled to the radio. Until this time, such batteries have typically been "two contact" devices such as the Motorola MX-300 battery 10 shown in FIG. 1A. That is, battery 10 includes a positive contact 20 and a negative contact 30. Contacts 20 and 30 are adapted to be coupled to corresponding respective contacts on the portable radio device (not shown) to which battery power is to be supplied. Battery 10 further includes battery charger contacts 40, 50, 60 and 70. In designating battery 10 as a two contact device, any battery contacts which are dedicated to coupling battey 10 to a battery charger are not counted.
FIG. 1B is a schematic diagram of the battery circuit which is contained within battery 10. Battery 10 includes a cell group 80 of six battery cells coupled together in series relationship. A positive terminal at one end of cell group 80 is designated terminal 80A. A negative terminal at the other end of cell group 80 is designated terminal 80B. Positive terminal 80A is coupled to battery contact 20 via intermediate circuitry discussed subsequently. Negative terminal 80B is coupled to battery contact 30.
To prevent battery 10 from overheating should contacts 20 and 30 ever be short-circuited, a thermostat 90 is coupled in series with positive terminal 80A and battery contact 20 as seen in FIG. 1B. Thermostat 90 provides an electrical connection below a certain threshold termperature and provides an open circuit above such threshold temperature. Thermostat 90 is selected to provide an open circuit condition when the temperature of battery 10 exceeds a first threshold temperature which is sufficiently high to indicate the presence of an improper operating condition. For example, thermostat 90 is selected to have a first threshold temperature of 85 degrees Celsius. Thus, when such first threshold temperature is exceeded, an improper operating condition is indicated which results in excessive battery temperatures. Then thermostat 90 opens and removes power from battery contacts 20 and 30.
To further protect battery 10 from high temperature improper operating conditions, a thermo-fuse 100 is coupled in series with a nichrome resistor 110 between contact 20 and thermostat 90 as shown in FIG. 1B. Resistor 110 is typically fabricated as a nichrome strip in conventional batteries. When excessive current is drawn from battery 10 through contacts 20 and 30, resistor 110 heats up. Resistor 110 is situated sufficiently close to thermo-fuse 100 that the heat it generates is transferred to thermo-fuse 100. At normal battery operating temperatures, thermo-fuse 100 exhibits a closed circuit. However, when the temperature of thermo-fuse 100 rises above a selected threshold level designated the second threshold level, then thermo-fuse 100 permanently changes from a closed circuit condition to an open circuit condition. The second threshold temperature is generally selected to be somewhat higher than the first threshold temperature associated with thermostat 90, such that should thermostat 90 ever fail to open when the first threshold temperature is reached, then thermo-fuse 100 would open when the second threshold temperature is reached to provide failsafe protection.
Battery contacts 40, 50, 60 and 70 are employed for charging battery 10. Battery contact 40 is coupled via a diode 120 to battery terminal 80A. It is seen that resistor 110, thermo-fuse 100, and thermostat 90 are also in line with diode 120 to provide protection against excessive battery temperature during battery charging. The polarity of diode 120 is selected to prevent cell group 80 from discharging into a battery charger (not shown) which is coupled to battery contacts 40 and 70.
A coding resistor 130 is coupled between contact 50 and terminal 80B which is designated as ground or reference. The value of resistor 130 is arbitrarily selected to indicate the capacity of cell group 80 to the battery charger so that the charger can send the appropriate magnitude of charging current to cell group 80. For example, assigning a value to resistor 130 of 500 ohms would indicate to the charger that cell group 80 exhibits a capacitor of 500 maH. Assigning a value of 1000 ohms to resistor 130 indicates that cell group 80 exhibits a capacity of 1000 maH. The charger, which is coupled to contact 50, senses the value of resistor 130, determines the capacity of cell group 80 and then sends the appropriate charging current to cell group 80 corresponding to the determined capacity of such cell group.
The battery charger which is coupled to conventional battery 10 must make a determination of when it is appropriate to discontinue charging. To facilitate this determination, battery 10 is provided with a thermistor 140 coupled between battery contact 60 and reference 80B. As battery charging progresses, the temperature of battery 10 rises until it reaches a temperature at which charging is complete. To proceed higher than this temperature would indicate that the battery is overcharged perhaps resulting in substantial battery damage. To prevent such overcharging, the charger is coupled to battery contact 60 to permit the charger to sense the resistance of thermistor 140 and thus determine the temperature of battery 10. When the charger determines that a battery temperature is reached which indicates that the battery is fully charged, then charging is discontinued.
Although conventional battery 10 permits a battery charger to determine certain battery parameters, namely charging capacity and charging temperature, battery 10 does not readily and efficiently permit a radio or other current consuming device coupled to main battery contacts 20 and 30 to determine battery operating parameters such as current drain due to operation of such radios or other device.